When one particle interacts with another it observes the other. Physical interactions between particles are in fact the only known way of making physical observations. As such, observation is inherently a symmetric action. You observing the reality around implies that that reality itself is observing you (masturbating.) However, there are strong physical limitations on particle interactions and observations. In particular, no particle not within your light cone of space (the space of particles that can reach you within the limits of the speed of light) can physically interact with or observe you. Logically, it therefore follows that no area of reality outside a light-year distance away from you can possibly have observed you masturbating until at least a year passes after you masturbating. So, while local areas around you such as the earth may be watching you masturbate there are vast amounts of space (perhaps infinite) that cannot watch you masturbate (at least not until vast amounts of time passes and you are dead.)